Check valves are devices that allow fluid to flow through a passageway in one direction but block flow in the reverse direction. They are used in a variety of applications. One of the many industrial applications for check valves is in reciprocating pump assemblies. Reciprocating pumps are used by field workers in various operations to pressurize a slurry mixture of solids and liquids and transfer fluids and mixtures from one station to another.
For example, reciprocating pumps are used in drilling operations to pressurize a slurry mixture of solids and liquids known as drilling mud to the bottom of a hole drilled into the earth. The pressurized mud is used to lubricate and cool a downhole drill bit as well as to carry loosened sediment and rock cuttings back to the surface. At the surface, the cuttings and sediment are removed from the returning drilling mud for examination and the filtered drilling mud is able to be reused. In many cases, highly abrasive particles are present in the fluids that are being pumped through the system. Because of these highly abrasive components, valves and seals of reciprocating pumps must be designed to resist harsh abrasion, while maintaining positive sealing action and withstanding high operating pressures.
A schematic diagram of a check valve supported reciprocating pump is shown in FIG. 1. In a pump of this type, a piston 21 reciprocates within a cylinder 20 in the direction shown by arrow 24. Check valves 22 are utilized at inlets 25 and outlets 26 of the cylinder 20 to restrict the flow of fluid to one direction. At fluid inlet 25, a check valve 22 is placed and oriented so that it only allows inward flow. At outlet 25, another check valve 26 is located so that it that only allows outward flow. The use of check valves 22 at pump inlets 25 and outlets 26 enables the pump to function in a much simpler fashion that does not require a timing or driving means to open and close the inlet 25 and outlet 26 valves at the appropriate times. Check valves 22 are often spring loaded so that at times of low or zero flow pressure, they are automatically shut. Effective check 410 valves 22 for pumping applications are also designed so that pressure in the back-flow direction contributes to the strength of the sealing mechanism.
For pump applications that utilize multiple check valves, it is preferred that all check valves be of the same design to ensure that the inlet and outlet flow characteristics of the pump are similar. Additionally, identical check valves allow the pump operator to carry fewer replacement parts, since he or she only has to carry parts for one type of valve. In many applications, it is further preferred that the check valves be unitized, or self-contained. A damaged unitized check valve can be easily removed from the pump assembly and replaced with minimal tooling and effort. Once the unitized check valve has been removed from the pump device, it can be disassembled and repaired if possible. By replacing check valves as units, expensive delays in operations can be minimized.
FIG. 2 shows a prior art unitized check valve that is typical of those used in reciprocating pump assemblies. The prior art check valve assembly 80 includes a valve body 81, a seal member 82, a biasing spring 83, and a spring retainer 84. The seal member 82 has a conical seal face 88 and guide legs 85 that facilitate the alignment within the valve body 81. The valve body 81 has a corresponding conical valve seat 87, and inner diameter 89, and rotary retaining tabs 90 for engaging the spring retainer 84. The spring retainer 84 has rotary retaining hooks 91 and fluid flow passageways 86. The rotary retaining hooks 91 of the spring retainer 84 correspond with the rotary retaining tabs 90 of the valve body 81 to form what is commonly referred to as a bayonet connector.
The check valve is assembled by placing seal member 82 into valve body 81, placing biasing spring 83 on top of seal member 82, placing the spring retainer 84 over spring 83 and compressing spring 83 until spring retainer 84 meets valve body 81, and engaging the bayonet connectors by turning retainer 84 clockwise with respect to valve body 81. Once assembled, seal member 82 is free to move up and down within the assembly while the guide legs 85 assure that when in the down position, the seal face 88 of the seal member 82 aligns properly with the valve seat 87. The valve design allows flow from valve body 81 through retainer 84 but prevents the fluid from flowing from retainer 84 through the valve body 81. The biasing spring 83 acts both to shut the valve during situations of low pressure and to maintain the tension required to keep the bayonet connection engaged.
It is preferred that all components of a reciprocating pump be designed so that the flow of the working fluid is as unrestricted as possible. Obstructions to fluid flow in the pump assembly can create fluid turbulence which increases the flow resistance of the fluid. By reducing flow resistance, a pump's efficiency, or ratio of work output to work input, can be increased. Increasing the efficiency of the pumping device reduces the costs of operation. In addition, because of the aforementioned abrasive particles existent in fluids, if prior art check valves are installed in solids laden pumping applications, they would experience a tremendous amount of erosion wear and fail prematurely. Hence, an effective check valve design for reciprocating pump applications should be able to withstand abrasive elements and maintain a tight seal.
The guide leg design of the prior art unitized check valve blocks the free flow of fluid from the valve body to the spring retainer and can cause undesirable turbulence. Also, the prior art design check valve includes a single biasing spring to compress the sealing member against the valve seat and to maintain the bayonet connection between the valve body and the spring retainer. In the event of failure or weakening of this biasing spring, the prior art valve can come apart during operation and damage the surrounding pump components. In order to prolong pump life and minimize operating costs, an alternative to the prior art design is desirable.